Antinuclear antibodies are autoantibodies, which means the body mistakenly produces these antibodies that act against normal substances in cells. Antinuclear antibodies or ANAs are autoantibodies that react to substances within the nucleus of the cell. Antinuclear antibodies can react to almost anything with the nucleus including DNA, centromeres, histones, ribosomes, and other nuclear proteins. The presence of ANAs in the blood may or may not provide evidence of autoimmune disease. ANA can be measured indirectly or directly. Indirect measurement of ANAs is done using immunofluorescence. Direct measurement of ANA is achieved with a solid phase assay, namely enzyme-linked immunoabsorbant assays (ELISA), fluorescent microsphere assays, or immunoline assays. In solid phase assays, a panel of antigens is used to detect specific antinuclear antibodies. A second antibody is used to detect autoantibodies that are bound to the test antigens. The presence of antibodies on the Direct ANA test is abnormal. Thus, anyone who receives a positive test has detectable antinuclear antibodies.
Normal Ranges for ANA Direct:
Normal is negative
Abnormal is positive
(Titer applies to indirect detection)
It is not possible to have Direct ANA levels that are too low. A negative result means that the person does not likely have a connective tissue disease or systemic rheumatic disease.
The presence of antibodies on the Direct ANA test may indicate an autoimmune disease, specifically a systemic rheumatic disease or connective tissue disease. In people with symptoms of connective tissue disease, Direct ANA can help confirm the diagnosis. A positive Direct ANA result alone does not necessarily indicate the presence of a connective tissue disease, however. This is especially true in patients who do not have symptoms of a connective tissue disease—a positive test indicates disease less in than 50% of cases.
Some specific causes of Antinuclear Antibodies are:
- Systemic lupus erythematosus
- Drug-induced lupus erythematosus
- Mixed connective tissue disease
- Rheumatoid arthritis
- Limited systemic sclerosis
- Polymyalgia rheumatica
- Systemic vasculitis
- Sjögren's syndrome
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